The present invention relates to the removal of adherent organic material from solid substrates, and more particularly to the removal of carbonized organic material from the surfaces of metal cookware.
The preparation of many baked and fried foods creates residue on the surface of the cookware that is comprised primarily of adherent organic material. Such material can be an adherent viscous or solid organic material, caramelized organic material or carbonized organic material. The removal of such materials has conventionally been done by abrasion or the use of chemically aggressive substances, such as solvents or caustic materials activated by heat.
Removing such materials by abrasion is labor intensive and can affect the surface of the material being cleaned. While chemical removal of adherent organic material from the surface of cookware can be done with a number of conventional chemicals, these materials are generally difficult to work with in that they cause skin or eye irritation, require heating of the surface to be cleaned or are corrosive to certain cookware, especially aluminum. Thus, the primary objective of the present invention is to provide a material that removes adherent organic material from the surface of solid substrates, such as cookware, that does not require heat, that is not toxic and does not generate irritating fumes, does not irritate the skin, and does not corrode aluminum cookware and is easily rinsed from the cleaned surface with water.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by the combinations particularly pointed out in the appended claims.
In accordance with the purpose of the invention as embodied and broadly described herein, the invention includes a solution for removing adherent, organic material from the surface of a solid substrate at room temperature. The solution comprises a first solvent, most preferably water, having dissolved therein up to 2% alkali metal silicates. The solution further includes a source of alkalinity that is substantially free of alkali metal hydroxide ions. The solution further includes at least one organic solvent in an amount up to 20%, and an amount of hydrotrope effective to render the organic solvent soluble in the solution. Up to 10% of amino alcohol is included in the solution. The solution also contains at least one surfactant in an amount up to 25%, and up to 15% of a corrosion inhibitor.
Another embodiment of the invention is a method for removing adherent organic material from the surface of a solid substrate at room temperature. In such an embodiment a solvent, preferably water, has dissolved therein up to 2% alkali metal silicates. The solution further includes a source of alkalinity that is substantially free of alkali metal hydroxide ions. The solution further includes at least one organic solvent in an amount up to 20%, and an amount of hydrotrope effective to render the organic solvent soluble in the solution. Up to 10% of amino alcohol is included in the solution. The solution also contains at least one surfactant in an amount up to 25%, and up to 15% of a corrosion inhibitor. Substrates, such as cookware, having adherent organic material are placed within the solution for a period of time effective to react with the adherent organic material and convert the organic material to a form that it can be readily removed from the substrate.
The solution of the present invention finds particular utility in cleaning the surface of aluminum cookware, and especially anodized aluminum cookware.
In accordance with the invention, there is provided a solution capable of removing adherent organic material from the surface of the solid substrate at room temperature. While such solutions are operable at room temperature and are advantageous because of there being no necessity to heat the system in order to provide a cleaning affect, heating of the solution may assist in the cleaning process. The invention includes a first solvent, the most preferred embodiment being water, with a combination of materials dissolved therein. While the invention has shown particular utility in an aqueous solution, the amount of solvent can be reduced but typically such solutions have no more than 80% water. More preferably, the water content should be no more than 75%.
The percentages set out herein are weight percentages, unless specifically set out otherwise.
In accordance with the invention, there is provided a source of alkalinity and that source should be substantially free of alkali metal hydroxide ions. Preferably, the source of alkalinity consists essentially of an alkali metal carbonate, examples being potassium carbonates, sodium carbonate, or mixtures thereof. The higher pH provided by the source of alkalinity contributes to the removal of the adherent organic material. Preferably, the overall solution has an alkaline pH less than 12, although a pH above 12 can be used where corrosion of the metal substrate is not an issue. In its most preferred embodiment, a water solution, the pH is preferably in the range of from 10 to 12, and most preferably about 11. In connection with the pH the word xe2x80x9caboutxe2x80x9d means plus or minus a pH value of 0.5. In the preferred embodiment, the alkali metal carbonate comprises from 5 to 11% of the solution and in the most preferred embodiment, approximately 9%. Amounts of alkali metal carbonate in excess of 11% are operable but are more corrosive to metals like aluminum. Higher concentrations of alkali metal carbonate may be used but the concentration of corrosion inhibitors would have to be adjusted if corrosion of the metal being cleaned was to be avoided.
It is important that the source of alkalinity not contribute an excessive amount of free metallic ions to the solution, as the presence of free metallic ions causes flocculation within the solution. While this may not always degrade the performance of the solution with respect to removing adherent organic material, it is not preferred. It is also preferred that the source of alkalinity include materials that serve as a good chelating agent to decrease the level of free metallic ions in the solution. Other sources of alkalinity, such as hydroxides, are not preferred for cleaning aluminum or anodized aluminum surfaces due to their propensity to corrode or attack the metal surface being cleaned and to increase skin irritation if the solution contacts humans or animals. Several sources of alkalinity, hydroxides in particular, also decrease the rinseability of the solution from the metal substrate being cleaned making rinsing of said substrate difficult and time consuming. For these reasons, hydroxides are not preferred for cleaning aluminum or anodized aluminum surfaces. Other sources of alkalinity other than carbonates include phosphates, borates, gluconates, silicates, and other salts of organic acids, as well as amines and amides.
In accordance with the invention, the solution includes at least one organic solvent in an amount up to 20%, and an amount of hydrotrope effective to render the organic solvent soluble in aqueous solutions. As here embodied, the organic solvent comprises one selected from the group consisting of dipropylene glycol normal propyl ether and N-methyl-pyrrolidone, in an amount of approximately 7% of a solution in the preferred embodiment. Dipropylene glycol normal propyl ether can be obtained from ARCO Chemical of Newtown, Pa., USA and is known commercially as Arcosolv DPNP. N-methyl-pyrrolidone is known commercially as NMP or m-pyrol and can be obtained from ISP Technologies Inc. of Wayne, N.J., USA. The function of the solvent is to promote the release of the organic material from the surface of the substrate being cleaned. One of the advantages of the present invention is that, in addition to emulsifying the adherent organic material, it removes such material from the surface of the solid substrate being cleaned by breaking the bond between the organic material and the surface of the substrate. While not wishing to be bound by theory, it appears that the solution delaminates the layers of the adherent organic material as well as breaking the chemical or physical bond of that material on the surface to be cleaned. In an aqueous solution, the solvent normally requires a hydrotrope to render it soluble in the solution. As will be discussed with respect to other components of the solution, many of them also have hydrotroping properties and assist in the dissolution of the organic solvent within the aqueous medium. Where a separate hydrotrope is used, it can consist essentially of sodium xylene sulfonate.
In accordance with the invention, the solution may include at least one corrosion inhibitor. As here embodied, the corrosion inhibitor can consist essentially of at least one fatty acid. Examples of fatty acids that can be used with respect to the present invention include caprylic acid and stearic acid. Other acids may include decanoic acid, lauric acid, dodecinoic acid, palmitic acid, myristic acid, and mixtures thereof. The fatty acids should be present in an amount up to 15%, with 2% being most preferred. Bicarbonates can also be used as corrosion inhibitors, alone or in combination with other corrosion inhibitors. The use of a corrosion inhibitor is particularly useful when removing adherent organic material from relatively reactive metal surfaces such as aluminum.
In accordance with the invention, an amino alcohol may be included to provide cleaning power to the solution. The amino alcohol is an emulsifier and helps loosen the carbon on the surface being cleaned. Preferably, the amino alcohol is present in an amount up to 10% of the solution, most preferably in an amount of 4%. Preferably, the amino alcohol is 2-amino-2-methyl-1-propanol. Such a material is known commercially as AMP-95 and is a product of Angus Chemical Company of Buffalo Grove, Ill., USA. Amounts in excess of 8 to 10% of amino alcohol are operable but raise toxicity issues with the solution. In certain applications toxicity may not be of concern, as for example cleaning or decarbonizing machine or engine parts, but in the preferred embodiment, the level of amino alcohol is such that there are no known significant toxicity effects and the solution can be handled without special precautions.
In accordance with the invention, the solution contains at least one surfactant in an amount up to about 25% to promote cleaning of the organic material from the surface of the substrate. As here embodied, the surfactant is an amphoteric surfactant that consists essentially of sodium lauriminodipropionate in an amount up to 2%. Such a material is known commercially as Mackam 160C-30, a product of McIntyre Group, Ltd. of University Park, Ill., USA. While the use of an amphoteric surfactant is preferred, anionic, non-ionic or amphoteric surfactants can be used.
In accordance with the invention, up to 2% alkali metal silicate can be included to provide corrosion protection to the metals being cleaned. As here embodied, the alkali metal silicate consists essentially of potassium silicate and in a preferred embodiment the potassium silicate comprises up to 0.25% of the solution. In such amounts the surface of the material being cleaned is not corroded and no significant amount of precipitates or flocculents are formed within the solution. Excess silicates in the solution may produce a heavy white stain on aluminum cookware that is undesireable. More importantly, the formation of undesirable silicates on the surface to be cleaned should be avoided as they are difficult to remove without the use of aggressive chemicals. In addition to potassium silicate, sodium silicates, or a mixture of potassium and sodium silicate can be used. In the embodiments tested the mixture of potassium and sodium silicate and use of sodium silicate alone produced more flocculent than potassium silicate alone. The presence of a precipitate or flocculent does not affect the performance of the solution, but its presence is not preferred.
An additional material that improves the performance of the solution by inhibiting attack or corrosion of the metal surface being cleaned is the presence of at least one phosphate ester. Phosphate esters are known corrosion inhibitors and examples of proprietary groups of products know to be operable are materials known as TMulz, a product of Harcroft Organics of Kansas City, Kans., USA, Rhodafac, a product of Rhodia Chemical Co. of Cranbury, N.J., USA and Chemphos, a product of Chemron of Paso Robles, Calif., USA. In addition, some phosphate esters are hydrotropes in the present invention. Bicarbonates are another material that can be used as a corrosion inhibitor. Bicarbonates buffer the system and prevent excessive free alkalinity.
As embodied herein the invention is a solution, and while its performance is not significantly affected by use (in other words the active ingredients of the solution are not consumed in the cleaning process), its performance is affected by the concentrations changing due to evaporation of the volatile ingredients, primarily the water and organic solvents. Thus, it is preferred to keep containers of the solution covered to prevent the evaporation of the water or organic solvents. In addition, as the solvents evaporate the silicate concentrations exceed the preferred amounts and flocculation or staining can result. Evaporation of the organic solvents also affects the performance of the solution for removing adherent organic material.
The present invention was used in connection with a number of examples, as set out below.